The Negative The quality of the writing in "Brisingr" is top-notch. However, in terms of plot and economy, the author seems to have gotten carried away. The characters are as interesting as ever, but the story drags — most notably, in the several chapters required to elect a dwarf king and the forging of Eragon's new sword. In Christopher Paolini's defense, he wrote this under shadow of the 2008 presidential election — perhaps that is why so much of "Brisingr" is spent on politics and philosophizing. On the other hand, the chapter dealing with the forging of the sword Brisingr is simply long and tedious. It may interest readers curious about medieval sword-making, but it's much longer than it needs to be and reads like a section from some kind of sword-making textbook. Still, one has to credit Paolini for doing his research.
Another criticism of "Brisingr" is the revelation of Eragon's true father. The series has had this Star Wars-like theme of parentage from the beginning of "Eragon"; "Eldest" revealed Morzan to be Eragon's father; and in "Brisingr" he discovers that his father was actually Brom. My personal reaction was to raise my eyebrows. I found it hard to believe that Brom, on his deathbed, wouldn't tell his own son his identity. Or that Oromis wouldn't, for that matter — or Saphira, since she knew as well. All in all, the premise on which the other characters concealed the truth from Eragon seemed thin. What this also does is further distance Eragon from his half-brother Murtagh, implying that Murtagh is doomed to his fate because his father was Morzan. And if Eragon ends up killing Murtagh in the last book, it will be more acceptable because they're simply following in their fathers' footsteps.
The Positive The writing is as strong as ever. Also, the romance between Roran and Katrina is very sweet without being overdone. The way in which Eragon and Arya's friendship grows closer — towards something more than friendship — is handled carefully and plausibly. Instead of throwing himself at her like he did in "Eldest," Eragon makes efforts to heal the rift created in their friendship by his romantic interest. The two grow to respect each other, and a romance doesn't look that far-fetched after "Brisingr." Other strong points of the book include the dragons' perspectives — for the first time, Paolini writes sections from Saphira and Glaedr's point of view. He also makes sure to show the ambiguity of stark definitions like good and evil, making it clear that Murtagh and Thorn aren't completely evil and Eragon, Roran and Nasuada aren't completely good.